This invention relates to a device and to a process for heating components of a microwave-absorbing plastic material, said device incorporating a microwave generator which generates microwaves of a particular frequency, an antenna which has at least one free end to which the microwaves are guided, and an enclosure surrounding and shielding the antenna, with a heating zone provided between the said free end of the antenna and the shielding enclosure in which zone the components can be heated in localized fashion.
In the conventional heating methods employed to date, the components are heated up by means of a heat reflector or an infrared heat source. However, heat reflectors or infrared heat sources of that type produce interference which leads to substantial measuring errors. It is for that reason that the quality of the components is not controlled directly by way of the process parameters but is instead determined indirectly by nondestructive or even destructive testing methods. These costly test procedures are employed for instance in the bonding of tubular components where the process parameters, i.e. the heat level and duration, are established on the basis of the material, the diameter and the wall thickness of the components. But such indirect determination of the process parameters complicates any systematic optimization of the bonding process since material-related and application-specific requirements cannot be considered in the equation, or inadequately at best.
An improved heating method involving the heating of the components with microwaves has been described in the as yet unpublished patent application DE 198 44 549 titled xe2x80x9cDevice and Process for Heating Microwave-Absorbing Plastic Componentsxe2x80x9d. That device and process offers a substantial advantage in that it is the first to permit the localizedxe2x80x94meaning precisely definedxe2x80x94heating of components. It opens up an entire array of possibilities for particularly efficient and thus quicker processing in terms of bonding, bending and cross-linking. Moreover, microwave heating of components offers the advantage of instant processing without any time delay.
Building on that state of the art, it is the objective of this invention to provide both an improved design concept and an improved process for heating microwave-absorbing plastic components, ensuring in simple fashion reproducible component quality.
In terms of the device, the objective is met by a design with the features specified in claim 1. Providing the device in the area of the heating zone with at least one microwave-unaffected temperature sensor for gauging the temperature of the component during the heating process, permits continuous temperature monitoring. Such temperature monitoring in turn makes it possible to ensure consistent quality of the heated components. One important factor is the fact that, in this type of component heating device, the microwave generator does not produce any interference for the temperature sensor, meaning that neither the microwave field nor the signal picked up and transmitted by the temperature sensor is subjected to any interference. Equally important, the microwave coupling system is not a source of interference for the temperature sensor since it does not itself heat up and therefore does not affect the temperature sensor in that respect.
Of course, depending on the configuration and size of the heating zone, the device according to this invention can be equipped with several temperature sensors for providing particularly comprehensive monitoring of the component temperatures.